Add support for limiting only rate in only one direction

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index e22f745469324ea4a355c5792f88ddec2ac90ef1..8f7320835c914ea54820a4b35330a8cb2d06205d 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -588,19 +588,29 @@ thinktime_blocks
                defaults to 1 which will make fio wait 'thinktime' usecs
                after every block.
 
-rate=int       Cap the bandwidth used by this job to this number of KiB/sec.
+rate=int       Cap the bandwidth used by this job. The number is in bytes/sec,
+               the normal postfix rules apply. You can use rate=500k to limit
+               reads and writes to 500k each, or you can specify read and
+               writes separately. Using rate=1m,500k would limit reads to
+               1MB/sec and writes to 500KB/sec. Capping only reads or
+               writes can be done with rate=,500k or rate=500k,. The former
+               will only limit writes (to 500KB/sec), the latter will only
+               limit reads.
 
 ratemin=int    Tell fio to do whatever it can to maintain at least this
                bandwidth. Failing to meet this requirement, will cause
-               the job to exit.
+               the job to exit. The same format as rate is used for
+               read vs write separation.
 
 rate_iops=int  Cap the bandwidth to this number of IOPS. Basically the same
                as rate, just specified independently of bandwidth. If the
                job is given a block size range instead of a fixed value,
-               the smallest block size is used as the metric.
+               the smallest block size is used as the metric. The same format
+               as rate is used for read vs write seperation.
 
 rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
-               the job to exit.
+               the job to exit. The same format as rate is used for read vs
+               write seperation.
 
 ratecycle=int  Average bandwidth for 'rate' and 'ratemin' over this number
                of milliseconds.
@@ -714,7 +724,9 @@ create_on_open=bool Don't pre-setup the files for IO, just create open()
                        when it's time to do IO to that file.
 
 pre_read=bool  If this is given, files will be pre-read into memory before
-               starting the given IO operation.
+               starting the given IO operation. This will also clear
+               the 'invalidate' flag, since it is pointless to pre-read
+               and then drop the cache.
 
 unlink=bool    Unlink the job files when done. Not the default, as repeated
                runs of that job would then waste time recreating the file